Process for cracking gas oils to gasoline



J. STEWART. ETAL 2,772,222

PROCESS FOR CRACKING GAS OILS To GASOLINE ZSIagetsShnat 1 Nov. 27, 1956Filed Nov 1%. 1953 Tail Gus+- Hydroformer -Nuphthu Heating 01 l K v w 9w 1 r ch Gas Frochonator H I 1 'IO N T Purge H DDG I LA I N (\IINVENTORS Jose ags'tewart, wv GmZmw wavless ATTORNEYH PROCESS FORCRACKING GAS OILS TO GASOLINE Filed Nov. 18, 1953 2 Sheets-Sheet 2 Nov.27, 1956 J. STEWART ETAL (\i .9 ll.

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W O G United States Patent CRACKING GAS OILS T0 GASOLINE ApplicationNovember 18, 1953, Serial No. 392,899

PROCESS FOR 3 Claims.

The present invention relates to the upgrading of hydrocarbon oils toproduce lighter and more valuable oils. It pertains particularly to animproved process for hydrogenating and upgrading gas oils, catalyticcycle oils or deasphalted oils boiling above the gasoline endpoint tothe more economically desired gasolines.

. Catalytic cracking of gas Oils and the like has been practiced formany years to produce gasoline. While catalytic cracking has provedimmeasurably valuable and has been much used as a means of satisfyingthe demand for high octane gasoline, it still is today a relativelyexpensive process and is so because of inherent limitations. There mustbe regeneration of the catalyst because of poisoning and carbondeposition. There must be replenishment of the catalyst because oflosses by attrition and failure of complete separation from products.The initial capital investments and operating costs for such a plant areusually high. It is apparent, therefore, that if a process can bedeveloped that can produce the same or nearly the same results as acatalytic unit for the same feed stock and does not involve the highinitial costs or the high operating costs of the catalytic unit, thensuch a process would be of considerable economic importance. Thisinvention makes possible a process that will obviate the necessity, incertain instances, of catalytic cracking of materials like gas oils inorder to upgrade them. This invention is based on the discovery-that itis possible to substitute hydrogen donor diluent cracking (HDDC) forcatalytic cracking in the process of upgrading gas oils when thegasoline produced is hydroformed.

The primary object of the present invention is to make possible theconversion of all, or substantially all, of a hydrocarbon material inthe nature of gas oil to more valuable gasolines. Another object is topresent a process that is more economically desirable than the presentmethod of producing high octane gasolines. An other more specific objectis to supplant the use of catalytic cracking steps in the process ofupgrading hydrocarbons. .A further specific object is to provide amethod to thermally upgrade oil stocks to gasolines when the gasolineproduced is hydroforrned. Further objects and advantages will appearmore clearly as this description proceeds. Reference will be made tospecific embodiments illustrated diagrammatically in the attacheddrawings which form part of the specification.

In the drawing- Figure 1 illustrates schematically the invention asapplied to the upgrading of a clear gas oil;

Figure 2 illustrates diagrammatically the process as it is used toconvert an oil requiring deasphalting.

Generally the process of this invention is carried out by mixing the gasoil feed with a recycled partially hydro genated oil fraction, boilingin the range of 400 to 950 R, which acts as a hydrogen donor. This donorcontains a substantial proportion of partially, but not completely,hydrogenated polynuclear aromatic compounds. After this treatment thematerial is fractionated to obtain gaseous hydrocarbons, gasoline, adiluent cut and heavy 2,772,222 Patented Nov. 27, 1956 "ice bottoms. Thegasoline fraction is hydroformed thereby increasing its octane ratingand producing hydrogen. The diluent cut is hydrogenated in the presenceof a suitable catalyst using the hydrogen created in the hydroformingstep. The process can be so operated so as to produce or consumehydrogen as may be desired. The hydrogenated diluent, along with theheavy bottoms, is then recycled to the hydrogen donor diluent crackingstep.

A co-pending application, Upgrading of Hydrocarbon Oils, Ser. No.365,335, filed July 1, 1953, by Arthur W. Langer, In, now abandoned,discloses the nature of the hydrogen donor diluents and their utility inthe conversion of heavy petroleum stocks to lighter, more valuabledistillate. The above application points out that it is not necessary touse substantially pure organic compounds as the donor diluent but thatheavy thermal tars make superior and inexpensive diluents. It furtherpoints out that incomplete hydrogenation of the tars is much moreefficient to effect conversion, i.. e., to hydrogenate petroleumcompounds. This invention is predicated upon the use of such a donordiluent. By this invention the conversion of relatively light petroleumfractions to lower boiling gasolines or naphthas is efiected without theuse of extraneous and expensive hydrogen. This hydrogen balance isobtained by removing hydrogen from the naphthas, produced by HDDC, byhydroforming, thus producing a high octane gasoline, and concurrentlyreintroducing the hydrogen by means of a donor diluent into the crackingstage thereby avoiding the formation of coke during the cracking.

It is possible according to the present invention to use the HDDCprocess in place of the catalytic process to convert a gas oil to agasoline when subsequently the gasoline is hydroformed. The mechanism ofthis invention can be envisaged by reference to thermal upgrading ofoils. Thermal cracking of oils, per se, has never proved practicable toprepare stock for subsequent catalytic reforming because at thetemperatures necessary to produce substantial gasoline portions manyunsaturates are produced. These unsaturates form gums and tars Whichrender the gasoline unsuitable for commercial use. Catalyticallyreforming such a gasoline results in high catalyst contamination and theproduction of relatively valueless products. In the present process thepresence of hydrogen donors during thermal cracking prevents theformation of such unsaturates by supplying readily available and easilytransferred hydrogen. Thus, the gasoline formed has the desiredcharacteristics for subsequent catalytic reforming.

In order to be effective the removal of hydrogen from the donor must besubstantially easier on the average than hydrogen removal from eitherthe aromatic or aliphatic fractions in the oil being converted.Available hydrogen-donor diluent, moreover, must be present in arelatively high concentration so that collision between the freeradicals, produced by the heat applied in thermal cracking, witharomatic or aliphatic molecules, is less probable than collision withdonor molecules. Moreover the dehydrogenated diluent must be such thatit or a good part of it can readily be recovered, rehydrogenated andrecycled.

As suggested above, prior art has mistakenly supposed that the morehydrogenated materials make the superior hydrogen donors. This has beenproved to be an erroneous and unwarranted assumption. A heavy oilfraction boiling above 500 F. up to about 1200 F., containingsubstantial and preferably at least major proportions of condensed ringaromatics and having added.

material suggested by prior investigators such as hydrogenated benzeneshow no activity at all for the purposes of the invention. Moreover pureor substantially pure compounds or hydrogenated compounds derived frompure compounds are usually relatively very expensive and their use ashydrogen donor diluents is not economically justifiable.

The following data, obtained by comparing the product of an ordinarycatalytic process and the process of this invention, will illustrate theutility of this invention.

Table I compares the products from a catalytic cracking process and thisprocess when the material treated is a deasphalted West Texas vacuumresiduum. It can be seen that the process of this invention competesfavorably with the catalytic cracking process.

Referring now to the drawings:

In Figure 1, the gas oil to be converted enters through line 1 where itis mixed with recycle bottoms from the fractionator 23 and ahydrogenated diluent from the hydrogenator 25, the bottoms and thediluent being conveyed by lines 3 and 4 respectively to line 2 whichadmits them to be mixed with the feed. The gas oil has a preferredboiling range of about 650 to 1000 F., but it may vary anywhere from 430F. to 1200 F. It may be virgin gas oil or gas oils from coking, thermalor catalytic cracking process. It should be relatively clean and forthis reason it may be necessary to deasphaltize the oil. The ratio ofmixing the diluent and feed components will vary with the history of thefeed, the amount of hydrogenation desired, the quality of the hydrogendonor and many other like factors. The ratio used may be varied from 0.1to 5.0 volumes diluent per volume of feed but a 0.1 to 1.0 ratio ispreferred. The reactants are suitably heated in a heater 21 and thenpassed via line 5 to the HDDC zone 22 Where the hydrogen transferoccurs. As depicted, a coil and drum arrangement is used but any othermethod of thermal treatment is quite satisfactory. The HDDC or thermalcracking step can be operated under conditions more severe than thoseused in the residuum process since the feed stock is lighter and thereis, therefore, less probability of coking. Suitable operating conditionsare about 850950 F., 2-5 v./v./hr. and 300-2000 p. s. i. g. By line 6the reactants are transferred to the fractionator 23 Where the productsare separated. Gas and a light fraction, e. g., C4 to C5 are by lines 7and 8 respectively removed and may be transferred to other processessuch as polymerization or may be consumed as fuel. Preferably, a lightnaphtha fraction boiling in the range of C5 to 200 F. is separated andremoved by line 27. It could, however, be hydroformed. A gasolinefraction boiling in the range of 200 to 430 F. is separated and sent tohydroforming unit 24 via line 9. A heating oil fraction boiling in therange of 430 to 650 F. can be removed by 26 as product as shown or canbe recycled to the feed as flux. If necessary, a diluent cut is made. Asdepicted here, this out has a boiling range of 650 to 950 F. It ispreferred that the diluent have this boiling range but the whole bottomsproduct can be used as the hydrogen donor if it does not have impuritiesdeleterious to the hydrogenation stage catalyst. Rather than use all thebottoms, a part only may be needed, which could be transferred by line11. If the total bottoms are recycled via line 3, then it may benecessary to purge some of it by line 18 in order to prevent excessivebuild-up of contaminants. It may be necessary to desulfurize thegasoline before hydroforming but in this illustration that step is notshown. Such desulfurization can be accomplished by any of several knownmeans.

The gasoline is hydroformed under suitable conditions and in thepresence of a catalyst. Such conditions may be 750 to 1150 F., 0.5-6.0w./hr./w. and 50 to 1000 p. s. i. g. The catalyst can be any of severalwell-known types but preferably a platinum or molybdena catalyst isused. The reformed gasoline produced is removed by line 12 and may be,as is indicated, blended with the C5200 F. fraction in line 27. Thehydrogen produced by the hydroformer is passed via line 13 to thehydrogenator where it is used to hydrogenate the donor diluent material.

The amount of hydrogen produced in the hydroforming step can becontrolled in part by proper regulation of temperature and propercatalyst selection. However, rather than sacrifice yield, virgin naphthacan be introduced via line 19 to control the hydrogen production. It canreadily be seen that by judicious control of temperature, catalyst andvirgin naphtha ratio and overall process can be made a balanced,consuming or producing one with respect to hydrogen.

The diluent cut may contain built up impurities and objectionableingredients which do not contribute to the hydrogen donor diluentfunction and therefore a purge line 16 is indicated. A make-up line 17is used to add a suitable diluent to oifset the purge and processinglosses. This make up tar can be obtained from other processes in acommercial refinery. The diluent is passed to the hydrogenator where itis contacted with the by-product hydrogen from the hydroforming step. Asmentioned, the donor diluent should be partially but not fullyhydrogenated. Hydrogen should be supplied to the hydrogenator at a rateof about 500 to 2500 s. c. f. per barrel of thermal tar fed to thehydrogenator. The hydrogen, after passing through the hydrogenator, ispreferably recycled to the hydrogenator via line 15. The unit isoperated at moderate pressure of the order of 500 p. s. i. g.Conventional temperatures are used and conventional catalysts,preferably of the sulfur insensitive type, such as molybdenum sulfide ornickel-tungsten sulfide are employed. There will be some tail gasproduced, removed by line 14, that can be used in other processes orconsumed as fuel.

For the above described process, if the feed amounts to 1000 bbl./day ofa virgin gas oil boiling in the range of 900 to 1100 F., the followingyields would be expected:

Internal Recycle diluent, 330 bbL/day, 650 to 900 F. boiling range.Recycle bottoms, 400 bbl./day, 900+ F. boiling range. Hydrogen fromhydroformer, 400,000 s. c. f./day. Gasoline from fractionator, 562 bbl./day, 65 to 430 F.,

boiling range.

External Gasoline, 465 bbL/day, 65 to 430 F. boiling range. Dry gas,450,000 s. c. f./day.

C4 fraction, 43 bbL/day.

Tail gas, 11,000 s. c. f./day.

Diluent and bottoms purge 20 bbl./day.

Referring now to Figure 2, a system is shown for converting an asphalticoil boiling above the gasoline range to lighter and more valuable oils.The feed enters the process through line 101 and is mixed with propane,furnished by line 102, in a conventional asphalt precipitator 130. Theconditions and manner of operation for propane deasphalting are wellknown to the art and need not be recited here. Although a propaneprecipitator is here shown any other suitable means of deasphaltingcould be used. The asphaltic phase leaves the precipitator through line104 and goes to a depropanizer 132 where the propane is separated andrecycled through lines 107 and 106 to the precipitator. The asphalt isremoved by line 105. The extract is taken by line 103 to anotherdepropanizer where the separation is eifected, the propane beingrecycled via line 106. The deasphalted feed is then mixed with therecycled hydrogenated tar, supplied by line 109, and the recycledbottoms, supplied by line 119, and fed to a heater 133 by line 108. Thereactants are then conveyed to the HDDC unit 134 by line 110. Theproduct leaves the unit by line 111 and is separated in fractionator135, here simply portrayed. The light gases are removed from thefractionator by line 112, hydrocarbons boiling below the gasoline rangeby line 113, naphtha boiling in the range of 65 to 650 F. by line 114, adiluent cut, if necessary, boiling in the range of 650 to 900 F. by line115 and a bottoms fraction by line 119. Again, if it is desired, all orsome of the bottoms can be hydrogenated by passing them through line 117to the diluent line 116.

If necessary, the gasoline fraction can now be desulfurized. Anyconventional means can be used such as hydrosulfurization, catalytic orextraction methods. Shown on the drawing is a caustic wash. The causticenters the desulfurizer 136 by line 121, flows downward countercurrentto the gasoline and leaves by line 122. After this treatment, thegasoline is passed by line 120 to the hydroformer 137 and aftertreatment is transferred by line 123 to subsequent blending orstabilization operations (not shown).

The diluent cut from the fractionator is passed by line 116 to thehydrogenator. Hydrogen from the hydroformer is added to the tar vialines 129 and 124. The hydrogenated tar is recycled to the depropanizedfeed by line 109. Hydrogen from the hydrogenator is recycled throughlines 126 and 124 or purged as spent gas by line 125. A diluent purge ismade by line 127 and replacement diluent from other refinery processesmay be added by line 128.

The above description and exemplary operations have served to illustratespecific embodiments of the invention. It is to be understood that theinvention embraces such other variations and modifications as comewithin the spirit and scope thereof.

What is claimed is:

1. A hydrogenation and reforming process for converting gas oils togasolines which comprises: mixing a gas oil feed with 1 to 5 volumes ofa hydrogen donor diluent and a recycled bottoms fraction, said hydrogendonor diluent predominantly comprising partially hydrogenatedpolynuclear aromatics boiling in the range of 650-950 F. derived from aheavy thermal tar; thermally cracking the resulting mixture in theabsence of a catalyst at a temperature in the range of 800-l000 F., aresidence time in the range of 2-5 v./v./hr. and a pressure in the rangeof 300-2000 p. s. i. g.; separating the cracked mixture into at least alight fraction boiling below gasoline, gasoline boiling up to about 650F., a spent diluent fraction boiling in the range of 650-950 F., and aheavy bottoms fraction; hydroforming said gasoline in thepresence of acatalyst at a temperature in the range of 750-l150 F., a residence timein the range of 0.5-6.0 w./hr./w. and a pressure in the range of -1000p. s. i. g., producing thereby a relatively higher octane gasolineproduct and by-product hydrogen; partially hydrogenating at least amajor portion of said spent diluent fraction in the presence of ahydrogenation catalyst with 500-2500 s. c. f. of hydrogen per barrel ofspent diluent fraction, a major portion of said hydrogen being composedof said byproduct hydrogen; and recycling and blending the partiallyhydrogenated portion with said feed.

2. The process of claim 1 wherein said gasoline obtained from thethermal cracking step is desulfurized prior to being hydroformed.

3. The process of claim 1 wherein said gas oil feed is obtained from adeasphalting operation.

References Cited in the file of this patent UNITED STATES PATENTS2,367,474 Stewart Jan. 16, 1945 2,381,522 Stewart Aug. 7, 1945 2,426,929Greensefelder Sept. 2, 1947 2,559,285 Douce July 3, 1951 2,642,381Dickinson June 16, 1953 2,703,308 Oblad et a1 Mar. 1, 1955

